1. Field of the Invention
The present disclosure relates to an organic light emitting diode display device. The present disclosure also relates to an active matrix organic light emitting diode display device and a method of fabricating the same.
2. Discussion of the Related Art
Although a cathode ray tube (CRT) has led the display device industry for several decades, the CRT has lost the lead in display devices by a flat panel display (FPD) due to a large volume and a heavy weight. In the display market, up to recently, the FPD has gained in popularity due to a light weight and a thin profile as compared with the CRT having a high resolution.
The FPD may include a liquid crystal display (LCD) device, a plasma display panel (PDP) device and an organic light emitting diode (OLED) display device. The LCD device has attracted wide attention and the OLED display device is getting the spotlight as a next generation FPD posterior to the LCD device. Specifically, the OLED display device has an emissive type to obtain a light weight and a thin profile as compared with the LCD device having a non-emissive type using a backlight unit.
The OLED display device may be classified into a top emission type and a bottom emission type. A light from an organic emitting layer is emitted through a cathode in the top emission type OLED display device and is emitted through an anode in a bottom emission type OLED display device. In the top emission type OLED display device, since the light is emitted through the cathode, a thin profile may be obtained. However, the cathode may have a high resistance.
In general, the OLED display device may include a substrate, a thin film transistor (TFT), a planarization layer, an anode, a bank layer, an organic emitting layer and a cathode. The TFT is formed on the substrate and the planarization layer is formed on the TFT. The anode is formed on the planarization layer and is connected to the TFT. The TFT transmits a source voltage according to a data signal to the anode and a current according to the source voltage is supplied to the anode.
The bank layer exposing a portion of the anode is formed on the anode and the organic emitting layer is formed on the bank layer and the exposed portion of the anode. The cathode is formed on the organic emitting layer. The organic emitting layer contacting the anode and the cathode emits a light.
In the top emission type OLED display device, since the light from the organic emitting layer is emitted through the cathode, the cathode should be formed to have a relatively small thickness. However, the thin cathode slows down a flow of a current due to a high resistance and causes non-uniformity in brightness. Accordingly, the cathode is required to have a relatively low resistance for a normal operation.